Fungistatic effects of purified conifer tannins against five wood-decaying fungi

Success of saprotrophic fungi in wood requires resilience against plant defences such as condensed tannins, but few studies quantify variability in fungal tolerance while using well-characterized defence compounds purified from authentic sources. To investigate the antifungal activity of condensed tannins, we quantified the bioactivity of conifer tannins from Scots pine (Pinus sylvestris) and Norway spruce (Picea abies) against five saprotrophs. Condensed tannins from conifer barks and from Scots pine needles showed moderate antifungal activities despite their low contents, and tannin structure affected their efficacy against fungi. Fungal sensitivity to condensed tannins was species-specific but did not vary systematically between rot types, indicating that specialization of brown-rot fungi on conifers does not imply better or worse tolerance to conifer tannins compared to non-specialized white-rot fungi. Despite the resilience of some saprotrophs, our analysis suggests generalized antifungal activity of condensed tannins against wood-decaying fungi.